1. Technical Field
The present invention relates to chairs, and more particularly to a multi-position adjustable arm for office chairs, which mounts directly to the bottom of the chair.
2. Background Art
A need exists for a multi-position chair arm adapted for vertical height adjustment, which permits a wide latitude in vertical positioning of the chair arm, is relatively easily manufactured, which is reliable in operation, and provides a wide variety of adjustable positions for the user. The chair design industry has heretofore provided a wide variety of chairs for the office environment which are ergonomically designed for the comfort of the user. Some of these chairs provide height adjustable chair arms, typically plastic assemblies fitted over plastic and metal supports that provide the structural strength for the chair arm assembly. These height adjustable chair arms typically utilize screw fastening systems and punched or slotted metal tube or brackets to provide engagement for the height adjustment mechanism. Many height adjustable arms which include a plastic height adjustment assembly on a metal substructure encounter problems with wobble and may rattle or feel loose, particularly at the top of the height adjustment range. The metal substructure is typically stamped steel with rough or sharp edges. The plastic housing quickly wears at the plastic to metal interface resulting in a loose and wobbling chair arm.
A further problem common with these type of chair arm assemblies is that the cumulative tolerances on the metal support width and thickness, paint coat thickness and tolerances of the molded plastic components all combine to create objectionable rattle and play in the final assembly. The difficulty of maintaining a tight fit between a plastic housing and a metal substructure results in excessive wear and unwanted movement or play from side to side and front to back, further resulting in rattle and noise.
Adjustable chair arms in the prior art lack height adjustment mechanisms which utilize a positive engagement locking mechanism. In the prior art, height adjustment mechanisms comprise several components, usually mounted pivotally on an inner wall of a sliding sleeve. In some of the prior art, these height adjustment mechanisms are in communication with a guiding slot and further comprise a portion with a lock pin biased with an integral leaf spring against an inner wall of the sliding sleeve to engage notches in the guiding slot in the support bracket portion of the arm. Shifting the lock pin along the guiding slot enables engagement of the lock pin with another one of the notches. Other height adjustment mechanisms in the prior art are in communication with a plurality of ratchet recesses spaced longitudinally along a support bracket and use a "ratchet dog", a biasing member for urging the ratchet dog into successive engagement with the plurality of ratchet recesses, and a means such as a movable slider for selectively displacing the spring to effect disengagement of the ratchet dog from the successive ratchet recesses. However, these arms have multiple pivotal components making them more difficult and expensive to manufacture.
Further, these arms wear from use, the arms fail to remain positioned at the desired detent, thus no longer working as a height adjustable arm.
Finally, traditional one piece plastic shells provide structural integrity as opposed to shells comprising a plurality of components; however, injection processes which form one-piece plastic shells by necessity of the molding process have draft angles, variances in the injected part making one end of the injected part smaller with respect to the other end, thus allowing the injected part to be removed from the injection mold. The draft angle of the one piece plastic shell induces a differential in tolerance of fit of the one piece plastic shell on the bracket onto which the one piece plastic shell is mounted; this differential, in turn, causes wobble in the arm assembly as the arm is raised on the bracket.